Kettle design WRT chilling & whirlpooling

[evoo4u]

After a few years of no-chilling, I've been pondering why my dark beers turn out better than pale ones.I think I have the answer - the dark ones are usually malt-driven, where as the pales I have been trying to brew are lacking the desired hop flavours and aromas. Without employing the Argon method and/or dry hopping, yesterday I used my new immersion chiller for the first time.

At FO, I re-circulated tank water through the 15 metres of 12mm copper tube, and achieved a rapid temperature reduction down to around 40C, but further reduction was very slow, even with regular agitation of the wort in the kettle. Which brings me to the topic of kettle design.

I use a 50 litre s/s keg, which is a substantial mass of metal, particularly around the base. This heated base ring, and the heat-soaked burner itself, keep adding heat into the wort despite running huge quantities of water through the chiller at around temp 24C. The full kettle is too heavy to lift off the burner and into a bath or similar, so I finally settled for a wort temperature of 30C before draining it into the FV. [ EDIT - I know I could employ a pre-chiller in an ice bath.That's maybe down the track]

Before draining it, I removed the immersion chiller and used the mash paddle to get a whirlpool going. Hot whirlpooling (with Brewbrite) has always worked well for me, but yesterday's low-temp effort was a failure. I've read about the benefits of high temp whirlpooling (aka poor whirlpooling at lower temperatures), but I'm wondering whether the small diameter and concave base of the kettle (keg) are contributing factors to the non-existent trub cone.

In summary: Would I have more success in chilling and subsequent trub-coning with a larger diameter, flat-bottomed kettle with less thermal mass?

Ideas?

 

[Lyrebird_Cycles]

Yes to not using a vessel with a concave base, no to worrying about the thermal mass.

Contrary to popular supposition, the specific heat capacity of steel is quite low. It's a weird thing that the volumetric heat capacities of most solids fall in a very narrow range from ~ 2 - 4 J / cm^3 / oK. Since steel is dense, this means the specific heat capacity of 304 SS is low, about 500J / kg / oK, which is a bit less than 1/8th that of water. Your keggle probably weighs about 10 kg, if so it has the same thermal mass as about 1.2 litres of water.

 

[evoo4u]

Thanks for the figures. It was an eye-opener that after 10 minutes or so, just how warm the base of the keggle felt, compared with the sides in contact with the wort.

 

[Coodgee]

When i used gas i used to hose down the outside to cool it down. The burner got quite a lot of surface rust but it didn't hurt it

 

[pcqypcqy]

Can't comment on the concave base issue as my kettle is a pot with a flat bottom, but I get good enough results with a bit of a stir with a paddle and then using a trub screen. I've been no chilling lately so this is all hot.

As you've touched on, the biggest issue when chilling is the last 10 or 20 degrees. The rate of chill (i.e. how fast the chiller removes heat from the wort) depends on the difference between the wort and tap water. As this difference reduces, so does the rate, and hence the time taken to get there increase. The only ways to overcome this are to use heaps of water (no issue if you're taking and returning to a tank or similar), and/or prechill the water.

I too have a chiller like you've just bought/made, and I'm thinking the optimum way to do this is to take some portion of it, cut it off, fashion this up as an inline prechiller between my pump and wort chiller, then put it in a white bucket with ice slurry or just a few frozen bottles/ice bricks.

Intuitively, as the chilling seems to stall at around 15 or 20 degrees above the incoming water temperature, if you can get a good ice slurry going and chill the chilling water to as close to zero as you can get it you should be able to chill directly to pitching temps reasonably quickly.

 

[evoo4u]

I too have a chiller like you've just bought/made, and I'm thinking the optimum way to do this is to take some portion of it, cut it off, fashion this up as an inline prechiller between my pump and wort chiller, then put it in a white bucket with ice slurry or just a few frozen bottles/ice bricks.

Intuitively, as the chilling seems to stall at around 15 or 20 degrees above the incoming water temperature, if you can get a good ice slurry going and chill the chilling water to as close to zero as you can get it you should be able to chill directly to pitching temps reasonably quickly.

I think by next brewday I'll bring the old chiller coil (the rectangular one) out of retirement. I used it before I became aware of No-Chill. I made it up to fit an iced-water filled 'Esky' and then drained the wort through the copper tube into the FV. It worked very well, and chilled 23 litres down to 18C in as long as it took to drain - about 5 minutes, but took a heck of a lot of ice. It should be a doddle to put this inline before the new chiller coil (centre), and achieve a not-quite-so-rapid chilling (as compared with all-ice), but using a lot less ice (and pleasing swmbo because there'll still be room in the freezer for food )

 

[pcqypcqy]

Yeah, if you have that ******* sitting in a slurry as a pre chill, you'll be laughing. One bag of ice would probably do it, or just even some ice bricks/frozen bottles if you didn't want to go buy ice each time.

 

[Lyrebird_Cycles]

A good rule of thumb is to treat the ice as though it was at -100 oC and apply the rule of mixtures.

This accounts for the enthalpy of fusion (333 kJ/kg) being equivalent to a temperature change of 80 oC (333 kJ/ kg / 4.18 kJ / kg / oC) and allows 20 oC for temperature shift (ice is normally stored at about -18 to -20)

 

[homebrewnewb]

...and then you are prepared to launch your rocket.

 

[evoo4u]

A good rule of thumb is to treat the ice as though it was at -100 oC and apply the rule of mixtures.

This accounts for the enthalpy of fusion (333 kJ/kg) being equivalent to a temperature change of 80 oC (333 kJ/ kg / 4.18 kJ / kg / oC) and allows 20 oC for temperature shift (ice is normally stored at about -18 to -20)

Despite not being an engineer , I actually made up a spreadsheet before I started no-chilling to calculate ice requirements, based on draining hot wort through my rectangular chiller coil. Was a good brain exercise!